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Chapter 22: Lower Respiratory Tract Infections

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AQ is a 44-year-old woman with a past medical history of hypertension and dyslipidemia. Medications include lisinopril and simvastatin. AQ has developed pneumonia and would like to take an oral agent that will not interact with her medications. Which of the following antibiotics used in the treatment of community acquired pneumonia is a strong inhibitor of the CYP-450 3A4 hepatic enzyme and would have a drug interaction with her medications.

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a. Azithromycin

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b. Clarithromycin

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c. Amoxicillin

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d. Cefpodoxime

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Answer b is correct. Clarithromycin is utilized for treatment of CAP, inhibits protein synthesis, and is a strong inhibitor of the CYP-450 3A4 hepatic enzyme. Therefore, drug interactions with the macrolide antimicrobial may be common. Medications that are substrates of the CYP-450 3A4 hepatic enzyme will have their metabolism/clearance decreased. Common examples of substrates of the CYP450 3A4 hepatic enzyme are the azole antifungals, calcium channel blockers (verapamil and diltiazem), and HMG-CoA reductase inhibitors, and many others.

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Answer a is incorrect. The azalide azithromycin is utilized for community-acquired pneumonia (CAP) and inhibits protein synthesis; however, it is a weak inhibitor of the CYP450 3A4 hepatic enzyme. Drug interactions are a major difference between the macrolides (erythromycin and clarithromycin) and the azalide azithromycin.

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Answer c is incorrect. Amoxicillin may be used as part of a treatment regimen for CAP; however, amoxicillin does not inhibit the CYP450 system.

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Answer d is incorrect. Cefpodoxime may be used as part of a treatment regimen for CAP; however, cefpodoxime does not inhibit the CYP450 system.

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Which of the following antibiotics has the same oral and IV dose? Select all that apply.

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a. Doxycycline

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b. Amoxicillin/clavulanate

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c. Piperacillin/tazobactam

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d. Ceftriaxone

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e. Ciprofloxacin

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Answer a is correct. Doxycycline is available in oral and parenteral formulations. The pneumonia dose of doxycycline for oral and IV utilization is 100 mg every 12 hours.

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Answer b is incorrect. Amoxicillin/clavulanate is available in an oral formulation only. Amoxicillin/clavulanate is available in immediate and extended release formulations. The immediate release dose of amoxicillin/clavulanate is 500 mg every 8 hours or 875 mg every 12 hours; the dose for the extended release preparation is 2000 mg every 12 hours.

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Answer c is incorrect. Piperacillin/tazobactam is available in a parenteral formulation only. The pneumonia dose of piperacillin/tazobactam is 3.375 g every 4 to 6 hours or 4.5 g every 6 hours.

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